Our field work is fundamentally challenging. We observe a large aquatic bird that spends much of its time underwater and surfaces unpredictably. With rare exceptions, individual loons are impossible to distinguish, so we must observe their colored leg bands to tell who is who. Thus, we can only conduct our research by obsessively monitoring leg bands when we can and matching what we see of leg bands with behaviors that the birds carry out. A typical field observation is: “Blue on right leg two-note wailed at 0643 while an eagle flew overhead more than 50 meters away — while the caller’s mate and chick were more than 20m away”, which would elicit a datasheet entry of “643twmc/EF” in the slot on the datasheet reserved for that loon. But sometimes important behaviors occur that we cannot assign to an individual loon. If we are only just approaching a pair when a behavior occurs, or have lost them between dives, we might have to make such an entry into a section of the datasheet entitled “Unknown Pair Member”. Such an entry would indicate that we knew that the caller was one breeder or the other, but could not be certain of identity. Naturally we try to minimize entries into the Unknown Pair Member field, as they reduce our capacity to quantify commitment to parental care and territory defense by the male and female.

To maximize the quality of our recorded observations, we carefully select contrasting color bands for pairs that we capture and mark. The breeders on Swamp Lake, for instance, are: FEMALE -> silver over red – right leg, orange over orange – left leg; MALE -> silver over yellow, mint over white. On Swamp, a quick glimpse of either leg of either pair member suffices to identify it, so we do well at assigning behaviors to the correct pair member.

Territorial evictions mess up our plan of having each breeder banded in a way that differs strikingly from its mate. When a new banded bird usurps a territory, its bands might happen to be quite different from those of its new mate or might not. Back in 2006, when a young male that we had banded as a chick (we term such loons “ABJs” for “adult banded as juvenile”) kicked the resident male off of the Oneida-East territory, the new pair had bands: FEMALE -> Silver over blue, orange over orange; MALE -> orange over orange, green over silver. It instantly became rather difficult to obtain good data on this pair, because they were skittish and because the occasional flash of orange color that we could see on a loon did not allow us to I.D. it unless we were certain of which leg we had seen.

Yesterday, Julia (pictured in her selfie above) reported our worst yet case of eviction leading to headaches in identification. Julia’s observations showed that “white with blue stripe over silver, green over green” had just evicted the resident male on Hilts Lake and paired quickly with the resident female, who is “silver over white with blue stripe, green over green”. Hence, the Hilts pair now consists of a male and female that are identical in the four bands on their legs and differ only in the transposition of the two bands on the right leg. Naturally, behavioral observations of this pair will be taxing for the observer — a real test of our ability to spot subtle differences in band combinations under field conditions. A great many observations of this pair will have to be dumped into the “Unknown Pair Member” box.

Often it is the unwelcome challenges in scientific research that can lead to advances in understanding. Loons do exhibit slight differences in details of the white stippled chin strap and the triangular patches of fine white stripes on the collar. Maybe photos we take of the Hilts male and female will reveal consistent differences in these markings that permit us to distinguish pair members there. I have long mused about the ability of the loons themselves to tell each other apart from a quick glance and without vocal cues. Perhaps the inconvenient turn of events on Hilts will spawn a new, more detailed look at how loons solve that essential but most vexing task — rapid visual discrimination between mates and territorial opponents.